Various discolorable ink compositions, which enable writing trace or a coating film formed by handwriting or printing on a paper to be decolorized by being heated or by using an organic solvent, have been proposed. The discolorable ink composition is useful for contributing to reuse of papers or useful for easy correction of errors in writing trace.
For example, Patent Literature 1 (JP 9-165537 A) proposes a thermally erasable ink composition prepared by dispersing a colorant, which is obtained by a reaction of a leuco dye with a developer to develop a color, and a decolorization agent in water.
Patent Literature 2 (JP 2001-123084 A) proposes a decolorizable pigment composition comprising a color developer, a color forming compound and a decolorizing agent, wherein the main component of the decolorizing agent in the composition exists in a microparticulate or microphase-separated state having a mean particle diameter of 1 nm to 100 μm when their shapes are approximately regarded as spheres in the colored state, and the main component of the decolorizing agent in the composition is molecularly dispersed in the composition in the decolorized state.
Patent Literature 3 (JP 5-87105 B) proposes an ink composition for ink jet printing which fades on heating, being prepared by dispersing, by mixing as separate particles, a resin composition comprising at least a heat-meltable water-insoluble resin of a melting or softening point of 60-180° C., a color former, and a volatile developer with a nonvolatile desensitizer of a melting or softening point of 60-180° C. or a resin composition containing this desensitizer.
Patent Literature 4 (JP 2005-89548 A) proposes a liquid composition having a thermosensitive color-changing property and a color-memorizing property comprising a microcapsule pigment and a vehicle containing a resin, wherein the microcapsule pigment occludes a composition having the thermosensitive color-changing property and color-memorizing property, which composition comprises a homogeneous compatibilized mixture of (1) an electron-donative color developing organic compound, (2) an electron-receptive compound, and (3) a particular ester compound as a reaction medium controlling the coloration reaction of the above (1) and (2).    Patent Literature 1: JP 9-165537 A    Patent Literature 2: JP 2001-123084 A    Patent Literature 3: JP 5-87105 B    Patent Literature 4: JP 2005-89548 A